This invention relates to improvement in dynamic sagittal knee test apparatus. Our prior apparatus described in U.S. patent application Ser. No. 005,921, filed Jan. 21, 1987, entitled, DYNAMIC SAGITTAL KNEE TEST APPARATUS disclosed a sagittal knee test apparatus that can measure knee laxities of a patient in both conventional test situations, wherein the patient is seated on a table and forces are applied to the knee at various leg extensions, or, can be utilized to measure knee and leg conditions while the patient walks in a normal manner. The advantage of such a device is described fully in our prior art application.
In summary, the apparatus for measuring ligamentous insufficiency in the knee enables a physician to provide a diagnosis of injury and/or an evaluation of different treatment methods. In the past, abnormal motion between the tibia and the femur was detected by a physician by manipulation of the leg by hand. Often the motion of a leg with a ligament tear is subtle and difficult to quantify or even compare with the patient's uninjured leg. Because a normal knee may have a substantial motion, it is desirable to quantitatively measure the precise displacement to allow an accurate comparison between the patient's normal and injured knee to determine the likely extent of injury. Further, it is desirable to quantify such measurements to compare motion of the patient's knee with statistical norms or with past records to monitor the progress of treatment.
Both our prior apparatus and the present apparatus are designed to be autoclavable or sterilizable by other methods. The apparatus is designed for use in both the 20.degree. Lachman test and 90.degree. anterior drawer test, and, without refitting is designed for use in measuring posterior excursions. It is believed that measurement of both anterior and posterior excursions provides the physician with the maximum useful data for proper diagnosis and treatment.
Our original mechanical device described in our patent No. 4,534,364 issued Aug. 13, 1985, entitled SAGITTAL KNEE TEST APPARATUS, provides an exoskeletal frame structure that permits comparative measurements to be taken from the light weight frame structure itself, thus freeing the patient from the chair as a reference point and improving the accuracy of measurements. It has been found, however, that measurements in addition to the anterior and posterior displacement are useful in accurately diagnosing the nature and extent of an injury. It is advantageous to measure varus-valgus laxity and axial rotation of the tibia relative to the femur. These additional measurements greatly enhance the ability to correctly determine the severity of injury and in particular whether it is the anterior cruciate ligament, medial collateral ligament or both that are damaged. Our apparatus as descried in the referenced patent application, Ser. No. 005,921, is designed to connect to the patient's leg at the long skeletal prominences with minimum restriction of normal joint motions. The framework is light in weight and mechanically self contained without mechanical connection to an external structure. The apparatus permits ambulatory motion to allow measurement to be obtained during normal movement such as walking as well as during conventional contrived, examination procedures where the leg is manipulated by hand or by special force measuring apparatus as disclosed in said application.
The present improvements relate to the dynamic sagittal knee test apparatus described in application Ser. No. 005,921, and enable the apparatus to be utilized with greater efficiency and ease. Since a prime source of diagnostic information is gained from comparative measurements of the patient's injured knee with the patient's uninjured knee, the sagittal knee test apparatus is frequently removed from one leg and installed on the patient's other leg. It is desirable to have this replacement accomplished as quickly and simply as possible. Furthermore, the complex linkage of the mechanism should be disturbed as little as possible such that accurate conparative tests can be accomplished. In our prior device, the linkage interconnecting the femoral frame and the tibial frame must be reconfigured when changing from varus-valgus tests to axial rotation tests. By integrating certain parts of the linkage, both axial rotation measurements and the varus-valgus rotations can be made at the same time, without having to reconnect the spanning linkage between the femoral mount and the tibial mount. In addition to simplifying the procedures that must be accomplished by the physician, the system allows for measuring to be accomplished in immediate sequence without readjustment of the equipment and potential change in the condition of the patient.
The improved spanning linkage has been devised to accomplish the three desired measurements without readjustment and has been constructed to make the measurements without being being affected by the polycentric motion of the knee during flexture. In this respect the improved linkage assembly incorporates the advantages of the prior assembly while eliminating its primary disadvantage.